The interaction of aging and hypertension will be studied in spontaneously hypertensive rats (SHR) and their normotensive controls (WKY). Having established the subcellular alterations during the development of cardiac hypertrophy and its prevention with antihypertensive drugs, future experiments will focus on the later stages of hypertension. We plan on utilizing acute hypoxia in order to ascertain whether differences in myocardial blood flow and capillary transport exist between SHR and WKY. Using ultrastructural stereology, we intend to complete the profile on the myocardial cell with reference of aging and sex. Further experiments utilizing ultrastructural cytochemistry are aimed at elucidating the mechanisms of degenerating changes observed near the end of the life span of SHR. The role of various antihypertensive drugs, e.g., alpha-methyldopa, chlorothaizide, hydralazine and reserpine, as well as blockers of protein synthesis will be studied in an attempt to clarify the relationship between blood pressure and cardiac hypertrophy. These studies will also be aimed at elucidating factors other than elevated blood pressure in the hypertrophic response in SHR.